264 ARUM MACULATUM AND ITS CROSS-PERTILIZATION. 
which, after again escaping, they perhaps carry to yet another 
a 
ecording to Darwin, Fabricius ss Sprengel net state that 
flies do not again escape from the flowers of Aristolochia when 
they have once entered; but this is obo usly aed as in that 
is 
e they ¢ not possibly assist the cross-fertilization 
It is perfectly certain that the aaanty y of flies escape, 
bu ertain that all do not do so owing 
very keen observation is given by Darwin.t He says:—‘‘On 
examining several spathes [of 4. bea , from thirty to 
sixty minute Diptera ogee to thre species were found in 
some of them; and many of these See were lying dead at the 
bottom, as if they had been shes ea entrapped. In order to 
discover whether the living ones could escape and carry pollen to 
another plant, I tied, in the spring of 1842, a fine muslin bag 
tightly round a spathe, and on returning in an hour’s time ees 
little flies were crawling about on the inner surface of the bag. I 
then gathered a spathe, and breathed hard into it; several flies 
crawled out, and all without exception were dusted with Arum 
pollen. These flies quickly flew away, and I distinctly saw three 
of them fly to another plant about a yard off; they alighted on the 
inner or concave surface of the spathe, and suddenly flew down into 
the flower. I then opened this flower, and sithoagh not a single 
anther had burst, several grains of ona were lying at the bottom, 
which must have been brought by one of these flies or some other 
insect. In another lower ‘ttle fies were crawling about, _— i 
w them leave pollen the stigmas.” That some of the 
ahoald die thus in the diabe seems very strange, and suggests the 
idea that the plant may have some other object, besides its cross- 
fertilization, in view in thus entrapping the flies; for it seems 
certain that every fly that dies in a flower lessens the chance of 
the 
secretion of the nectar, and certainly they often do so before the 
shedding of the pollen. On the evening of April 12th, 1882, Mr. 
Christy eee two flowers, both of which were devoid of heat or 
smell, but the pollen was not shed. One contained about one 
hundred live hie and the other thirty live ie two dead ones. 
sec flower, rather more advanced and with all the pollen shed, 
seems, from a note kindly sent us by Mr. Bennett, that G. Kran us has 
tested the eley ation of temperature, &c., in Arum italicum, and found that e 
thermom eter Pete in the midst = five opening < scia rose from 17°7 
44 eating commenced at the apex “ the spadix, where it was mos be 
considerable, and proceeded eo alae rds. The rise of “a perature in the anther 
takes place much later, and is less considerable; "ee stigmas experience no rise 
at all. It wou ald be interesting to compare the eer af the means of a 
tilization of drum maculatum, as given above, with the description of that 
hia Clematitis, as given by Mr. aeiets (Pop. Sci. Rew: April, 1875, p. a: 
+ ‘Cross and Self-Fertilization of Flowers, p. 417. 
